1. Field of the Invention
The present invention relates to the biological control of plant diseases (e.g. either pre-harvest or postharvest diseases) in agricultural commodities such as fruit. More particularly, this invention relates to: (1) methods for biologically controlling plant diseases (such as post harvest rots) on agricultural commodities using either, (a) at least one calcium salt and at least one microorganism which is an antagonist to plant pathogens, or (b) at least one microorganism which is an antagonist against plant pathogens but is not antibiotic; (2) compositions useful in such methods, and; (3) manufactures produced by such methods.
2. Description of Prior Art
Postharvest diseases of fruit cause 15 to 25% losses yearly in the fruit industry worldwide. Fungicides, the major weapon in combatting these diseases, are often ineffective and pose hazards to humans and the environment. Therefore, a critical need exists for new methods to control postharvest diseases without posing such hazards to humans or the environment.
Recently, it has been shown that the postharvest treatment of fruit with antagonistic microorganisms is an effective approach to the control of postharvest rots. Remarkable success was shown in the control of brown rot in peaches caused by Monilinia fructicola (Wint.) Honey with Bacillus subtilis. Pusey et al. [Plant Dis. 86:753-756 (1986)]. De Matos was able to reduce mold incidence from 35% to 8% when a species of Trichoderma was inoculated with Penicillium digitatum into lemon peel. De Matos, Ph.D. Dissertation, University of California, Riverdale, (1983). Singh and Deverall demonstrated biocontrol with bacterial antagonists to the citrus pathogens Alternaria citri Pierce, Geotrichum candidum link. ex Pers., and P. digitatum. Singh et al. [Trans. Br. Mycol. Soc. 83:487-490 (1983)]. Dipping wounded citrus fruit in suspensions of bacterial cells, particularly a strain of Bacillus subtilis (Ehrenber) Cohn, delayed decay by the three rot pathogens.
A first aspect of the present invention relates to processes for inhibiting plant pathogen development on an agricultural commodity comprising: applying (in the context of the present invention, xe2x80x9capplyingxe2x80x9d is intended to be limited to the intentional and willful dispensing of the microorganism(s) onto the agricultural commodity, as opposed to the natural occurrence of a microorganism on an agricultural commodity) to an agricultural commodity at least one microorganism, the at least one microorganism being an antagonist against plant pathogens but not being antibiotic, wherein the at least one microorganism is applied in an amount effective to inhibit plant pathogen development on the agricultural commodity. The most striking and novel aspect of this invention is the use of microorganisms which. do not produce antibiotics to control the diseases of agricultural commodities. This method is of importance to the consumer because it avoids the potential adverse effects of antibiotics in the food supply, such as the development of antibiotic resistance in human pathogens.
A second aspect of the present invention relates to processes for inhibiting plant pathogen development on an agricultural commodity comprising: applying to the agricultural commodity at least one calcium salt and at least one microorganism which is an antagonist against plant pathogens (and preferably not antibiotic); wherein the at least one calcium salt and the at least one microorganism are applied to the agricultural commodity in an amount effective to inhibit plant pathogen development on said agricultural commodity.
A third aspect of the instant invention pertains to compositions which maybe utilized in carrying out the aforementioned processes. Such compositions include:
A composition comprising a mixture of, (1) at least one microorganism which is an antagonist against plant pathogens but is not antibiotic and, (2) a carrier for said at least one microorganism selected from the group consisting of a gel, gum, wax, oil, talc, starch and mixtures thereof;
A composition comprising a mixture of, at least one microorganism and a carrier for said at least one microorganism, wherein at least 99% by count of said at least one microorganism is antagonistic against plant pathogens but is not antibiotic; and/or,
A composition comprising a mixture of, at least one calcium salt and at least one microorganism which is an antagonist against plant pathogens, and preferably is not antibiotic (preferably such a composition may: (a) consist essentially of the at least one calcium salt and the at least one microorganism, and/or; (b) have at least 99% by count of microorganisms therein be antagonistic to plant pathogens, and/or; (c) have at least 99% by count of microorganisms therein be nonantibiotic).
A fourth aspect of the present invention relates to manufactures which may include:
A manufacture comprising an agricultural commodity having thereon a concentration of at least about 105 colony forming units per square centimeter of at least one microorganism which is an antagonist against plant pathogens but is not antibiotic;
A manufacture comprising an agricultural commodity having microorganisms thereon, wherein the majority of said microorganisms are at least one microorganism which is an antagonist against plant pathogens but is not antibiotic;
A manufacture comprising an agricultural commodity having thereon a calcium salt and at least one microorganism which is an antagonist against plant pathogens (and preferably is not antibiotic) in a concentration of at least about 105 colony forming units per square centimeter; and/or
A manufacture comprising an agricultural commodity having a calcium salt and microorganisms thereon, wherein the majority of microorganisms on said agricultural commodity are at least one microorganism which is an antagonist against plant pathogens.
A fifth aspect of the present invention relates to a biologically pure culture of an isolate of Hanseniaspora uvarum having the identifying characteristics of isolate NRRL Y-18527.
The aforementioned microorganism(s) may for example be selected from the group consisting of: fungi (e.g. yeast), bacteria, viruses and mixtures thereof.
In regard to a preferred embodiment of the present invention, we have discovered new strains of yeast that are highly effective in controlling a variety of plant (e.g. fruit-rot) pathogens which affect a wide variety of agricultural commodities. Three isolates of the new strains have been deposited with the culture collection at The Northern Regional Research Center, U.S. Department of Agriculture, Peoria, Ill. 61604, under the acquisition numbers NRRL Y-18313, NRRL Y-18314 and NRRL Y-18527. NRRL Y-18314 has been identified as Pichia quilliermondii and NRRL Y-18527 has been identified as Hanseniaspora uvarum (Nidlaus) Shehata, Mrak et Phaff. The deposited materials have been accepted for deposit under the Budanest Treaty on the International Recognition of the Deposit of Microorganisms for the purposes of patent procedure. Further, (1) said depository affords permanence of the deposits and ready accessibility thereto by the public if a patent is granted, (2) the materials have been deposited under conditions that assure that access to the materials will be available during the pendency of the patent application to one determined by the Comissioner of Patents and Trademarks to be entitled thereto under 37 CFR 1.14 and 35 USC 122. All restrictions on the availability of progenies of the strain to the public will be irrevocably removed upon the granting of the patent.
Accordingly, it is an object of the present invention to provide novel biological control agents which pose no risk to the consumer and are highly effective in controlling a variety of plant pathogens causing preharvest and postharvest diseases on a variety of agricultural commodities (e.g. fruits).
It is also an object of the invention to provide a method of biologically controlling plant diseases (e.g. postharvest diseases) on agricultural commodities (e.g. fruits) which does not require the use of fungicidal treatments.
In a preferred embodiment of our invention, agricultural commodities are subjected to an aqueous suspension comprising an isolate of yeast having the identifying characteristics of an isolate selected from the group consisting of: NRRL Y-18313, NRRL Y-18314, NRRL Y-18527 and mixtures thereof. In effect, the organisms multiply and occupy the surfaces of wounded fruit, thereby preventing infection by plant (e.g. fruit-rot) pathogens.